The NFL is a gladiator sport. Players put their lives and well being on the line each and every week. Over the years, athletes have grown faster and become stronger. The league says it has never been safer than it is today. Concussion awareness has reached an all time high. Still, the violence of the game cannot be completely eliminated – nor should it be. Like it or not, it’s established the league as America’s favorite sport.

A recent study by the University of Michigan monitored Division I players using a custom-fitted device on their shoulder pads. The study measured intensity and number of impacts using G-forces. For context, 5 G's of force is equivalent to a racecar braking and turning.

According to the numbers, running backs experienced the most impacts over 10 G’s. This is likely the result of gang tackles and head-on hits. Compared to running backs receiving the harshest individual hits, wide receivers and offensive lineman experienced light collisions more frequently. On the other side of the ball, defensive tackles partook in the hardest hitting clashes.

These numbers and forces came from college athletes. The damage only multiplies when applied to the supreme athletes in the NFL. Regardless of position, a few particular players seem more prone to bruising hits. Moving past the science and G-forces, here are the Top 15 NFLers Who Take the Most Vicious Hits.

15 Eddie Lacy

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Eddie Lacy exploded onto the scene as Green Bay’s rookie running back in 2013. His vicious running style resulted in 1,178 yards and 11 touchdowns. Lacy won the NFL Offensive Rookie of the Year Award. His early success on the ground came with a toll. He suffered two concussions in his first seventeen games. The second came after Lacy initiated helmet-to-helmet contact with hard-hitting safety Kam Chancellor, leading Lacy to make a switch to his old helmet following his second concussion. He also recognized a need to alter his bruising style in the future to avoid harsh collisions. Lacy’s detractors may claim the running back’s alteration strategy somehow involved eating himself out of shape. Lacy had an abysmal 2015 season, managing only three touchdowns and 758 rushing yards. Although his speed and elusiveness took a hit, Lacy still makes a living between the tackles and remains one of the most physical halfbacks in the league.

14 Robert Griffin III

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The league’s best rookie a season before Lacy makes the list for the opposite reason. While Eddie Lacy welcomes and creates contact, Griffin cannot seem to withstand hits at the NFL level. His recent shoulder fracture is par for the course for both Griffin’s career and the soul crushing Cleveland franchise. The Brown bypassed drafting a quarterback in favor of signing Griffin to a $15 million contract over the offseason. Griffin broke his shoulder during a week one loss to the rookie Cleveland could have drafted at No. 2, in Carson Wentz.

Back in his impressive rookie season, RGIII suffered an LCL Sprain in week 14, followed by a torn LCL, ACL and meniscus in that year’s Wild Card game. Mike Shanahan benched him for the last three games of his sophomore season, citing concerns over Griffin’s long-term health. RGIII dislocated his ankle in 2014 and suffered a concussion during the Redskins’ 2015 preseason. He never quite mastered the art of the QB slide. Griffin’s gawky frame has made him an easy target for punishment over the course of his five-year career.

13 James Harrison

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Only three things in life are certain: death, taxes, and the fact that the Pittsburgh Steelers will regularly employ a beast at the linebacker position. James Harrison, the 38-year-old outside linebacker, has been exactly that in two different stints with Pittsburgh. This article might seem like it caters to offensive players, but the other side of the ball deserves attention as well. The hits defenders deliver wreak havoc on their bodies. Harrison has been at it for 14 years. He remains an integral part of the Steelers’ defense at an age that most linebackers have long retired. Harrison manages to remain physical due to his insane workout regiments (often posted on his Instagram). Aside from being a looming presence to offenses everywhere, Harrison takes glee in enforcing the cutthroat Steel Curtain mentality. His play over the years has led to over $200,000 in fines. This makes him one of the hardest hit players in both on-field action and off the field penalties.

12 Clay Matthews

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Both Clay Matthews and James Harrison were recently cleared of any wrongdoing involving the use of performance-enhancing drugs, after an Al Jazeera documentary appeared to implicate them. Both also belong among the NFLers involved in the hardest hits. Matthews is a blur on the field, switching seamlessly between outside and inside linebacker. Now in his eighth year, Clay has been named to the Pro Bowl six times thanks to his eye-popping defensive hustle and he currently has 69.5 career sacks. Matthews’ style of play is polarizing. He’s the type of player fans only love on their own team,and he’s had his fair share of “dirty” accusations. One late hit on Colin Kaepernick drew the ire of many during 2013’s opening week. Clay responded to criticism saying, “I’m an awesome player, not a dirty player.”

11 Rob Gronkowski

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Rob Gronkowski endures collisions as both a receiver and blocker, compounding the impact on his body. Standing 6’6” and 265 pounds, Gronk is a physical freak and a matchup problem for defenses. He dishes as much punishment as he receives, but the grueling life of an NFL tight end has certainly affected him. Gronkowski still hasn’t played a game this season after pulling up lame with a hamstring injury in practice. Beginning with back surgery during his college career, the tight end’s approach to the game has resulted in several major injuries. He fractured his forearm and later underwent four surgeries to clear an infection. His 2013 season ended after a low hit tore his ACL and MCL. Despite a plethora of health issues from big time hits in his career, Gronk remains the cream of the crop in both skill and physicality at the tight end position.

10 Wes Welker

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Fun fact: Wes Welker is still a free agent and has not retired from the NFL, perhaps because he’s forgotten to do so after multiple concussions. At one time, the league’s premier slot receiver, Welker played for five teams and had 903 catches in his career, while leading the league in receptions in 2007, 2009 and 2011. The combination of Welker’s small size and his proclivity for underneath routes has resulted in numerous jarring blows. Most notably, Welker once suffered three concussions in ten months, two of which occurred over a four game span. Champ Bailey hoped Welker would retire in 2015 because of the concern over his former teammate’s health, but Wes went on to play eight games with the Rams, accumulating 13 catches for 102 yards. It remains to be seen if Welker makes an appearance for a receiver-needy team this season.

9 Kam Chancellor

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When Kam Chancellor was a senior at Virginia Tech, he was entrusted with carrying the team’s symbolic lunch pail to every game. The pail signifies the Hokies’ blue-collar mentality. Chancellor has brought that same attitude to Seattle and has become a significant member of The Legion of Boom. He embodies the group’s name in every way and is known as one of the hardest-hitting safeties in the NFL. When Chancellor held out until September 23rd during the 2015 season, Seattle’s defense certainly showed evidence of a missing link, though Chancellor claims he wants to stay in Seattle despite the failed contract negotiations. This is the best case for both parties. Chancellor does not possess amazing coverage skills. Being surrounded with talent at the cornerback position allows him to do what he does best – crack any ball carrier in sight.

8 Anquan Boldin

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The ageless veteran joined his fourth team, the Detroit Lions, to begin his fourteenth season in the league. In a league of tough men, Boldin’s toughness is nearly unmatched. He plays through injuries, lays his body on the line and delivers results. 14 years and over 1,000 receptions leave plenty of opportunities for nasty hits, but nothing displays Boldin’s grit more than his 2008 season with the Cardinals. In the closing moments of a 56-35 loss to the Jets, Boldin was on the receiving end of a brutal helmet-to-helmet demolition by safety Eric Smith. Both players suffered a concussion. Boldin required surgery for a facial fracture and needed wires inserted in his lower jaw to correct his bite. He refused pain medication, opting for ice packs instead. The doctors projected his return at six to eight weeks. Boldin worked out one week after surgery and returned to field action in three. The scare didn’t change him and Boldin’s physicality remains a staple of his game.

7 Frank Gore

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Frank Gore is the oldest starting running back in the league (33) and the active leader in rushing yards (12,143). He spent the majority of his prime with an anemic offense and Alex Smith managing games. Defenses knew what to expect from San Francisco and stacked the box to prevent Gore from gashing them, but it never really worked. Never a speedster – his 40 time was 4.58 – Gore gained most of his yards by running through his opposition. The back suffered two significant injuries during his career that stemmed directly from contact. He fractured his hip in 2010. The 49ers actually had to hide his helmet to prevent him from returning to the game. He also became concussed after a block on Seahawks linebacker Bobby Wagner in 2014. The tough sledding didn’t get any easier in his first season with Indianapolis. Andrew Luck missed most of the season, ridding Gore of the chance to play with a feared quarterback behind center.

6 Jason Witten

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Jason Witten has demonstrated remarkable durability throughout his career. He’s a throwback footballer with modern day receiving skills, quietly amassing the second most receiving yards of any tight end in NFL history. Witten is 34-years-old and entering his fourteenth season, playing 16 games in all but his rookie season. That year, after fracturing his jaw in October, he only appeared in 15 games. How soft, right?

Witten lacerated his spleen during the 2012 preseason. He recovered by opening day and finished the year with his fourth (and most recent) 1,000 yard receiving season. If there are somehow lingering doubts about his toughness, look up “Jason Witten runs without helmet.” You’ll find a week 9 play against the Philadelphia Eagles. Witten caught a pass on the Eagles’ 35-yard line and, a split-second later, the defender launched headfirst into Witten’s facemask. A second Eagle ripped Jason’s helmet off. As payback, Witten chugged down to the Eagles’ 6-yard line sans headgear.

5 Ben Roethlisberger

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Ben Roethlisberger seems to experience at least one injury scare every season. One of the league’s foremost gluttons for punishment, Big Ben should still be considered durable. He’s never played less than 12 games in a season. His injuries stem from sacks and improvisation, as Big Ben is a wizard when the play breaks down. However, he’s doesn’t escape with his legs as often as Aaron Rodgers or Cam Newton, but simply takes the hits and refuses to go down until he can unleash some inconceivable bomb, likely to Antonio Brown. Big Ben’s ability to prolong plays has moved him into 8th all time with 441 sacks. To put the number in perspective, that’s 112 more sacks than Philip Rivers and 130 more than Eli Manning, both drafted the same year. Big Ben is a rare breed of signal caller that can absorb such frequent sacks. He’s a tank at 6’5” and 240 pounds, but the wear and tear is getting to him. 2015 saw Big Ben carted off the field twice – once for a knee sprain and once for a mid-foot sprain, but he still played in 12 games.

4 Ndamukong Suh

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The defensive position with the highest recorded hits in the University of Michigan’s study deserves representation from the most overly aggressive player in football. Like James Harrison, Suh has heard from the league’s discipline office frequently. At this point, he should prepare for each season by writing a blank check to Roger Goodell. Nearly ten years younger than Harrison, Suh has securely assumed the mantle of the NFL’s most vilified player. He’s been fined for roughing the passer, making a throat-slashing gesture, throwing an egregiously low block, stomping a lineman’s arm, and unnecessary roughness. He stays employed because he possesses the explosiveness to be a generational talent, as Suh pushes the line and punishes weaker players. His fiery persona translates into hard hits that affect both himself and the victim.

3 Julian Edelman

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The NFL is a copycat league. After New England’s success with Wes Welker, general managers scoured college football to uncover a similar player. The Patriots located a Welker clone more successfully than anyone. A few inches taller, Edelman is the best option route runner in the NFL and shares effortless chemistry with Tom Brady. His route tree, however, leaves him susceptible to collisions and injuries. He’s played in all 16 games only once. Over the course of seven seasons, Edelman has been diagnosed with several concussions. He’s fractured his forearm, hand (twice) and foot. Edelman has returned double digit punts in every season since his rookie year. The returner role exposes Edelman to special teams players with a full head of steam. Now, the Patriots are down to their third string quarterback for a week 3 matchup against Houston. Belichick has not signed anyone and plans to use Edelman as a second string quarterback. At least he wouldn’t be getting flattened on a crossing route.

2 Adrian Peterson

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Adrian Peterson has always mixed speed with tackle breaking abilities. He’s unquestionably the most dominant running back in an era of backfield committees. An every down player, Peterson has tallied over 300 carries four different times in his career. He has never rushed for less than 1,000 yards during a season in which he played more than 12 games. Even in the 12-game season (2011), his pace would have been good for just under 1,300 yards with a full campaign. Basically, Adrian Peterson runs hard. With that much mileage, Peterson has faced his share of big collisions and Father Time is coming. Peterson is on the wrong side of 30. In a small 2016 sample size, his violent history in the backfield has crept up on the future Hall of Famer. He averaged 1.6 yards per carry in two games before hurting his meniscus in a win over the Green Bay Packers. Time will tell if he recovers and regains form, but it’s ticking either way.

1 Cam Newton

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Cam Newton finally arrived as one of the game’s true superstars last season, throwing 35 touchdowns and adding 10 more with his feet. He won the MVP award and led Carolina to the NFC Championship. All that is missing from his star power is the calls that normally come with it. The NFL’s 2016 opener between Carolina and Denver acted as a microcosm of the referee’s treatment toward Newton in 2015. Newton received numerous hits to the head during the game and the only roughing the passer call the whole night was nullified by an intentional grounding. During his MVP season, Cam Newton did not receive a single roughing the passer call. Newton likely misses out on penalties due to his prowess as a runner, but that doesn’t mean the hits aren’t coming. Even if his placement at number one partly stems from recency bias, Newton consistently opens himself to danger both inside and outside the pocket.